Current indications and surgical strategies for myocardial revascularization in patients with left ventricular dysfunction: a scoping review

Background Ischemic cardiomyopathy (ICM) accounts for more than 60% of congestive heart failure cases and is associated with high morbidity and mortality rates. Myocardial revascularization in patients with left ventricular dysfunction (LVD) and a left ventricular ejection fraction (LVEF) ≤35% aims to improve survival and quality of life and reduce complications associated with heart failure and coronary artery disease. The majority of randomized clinical trials have consistently excluded those patients, resulting in evidence primarily derived from observational studies. Main body We performed a scoping review using the Arksey and O'Malley methodology in five stages: 1) formulating the research question; 2) locating relevant studies; 3) choosing studies; 4) organizing and extracting data; and 5) compiling, summarizing, and presenting the findings. This literature review covers primary studies and systematic reviews focusing on surgical revascularization strategies in adult patients with ischemic left ventricular dysfunction (LVD) and a left ventricular ejection fraction (LVEF) of 35% or lower. Through an extensive search of Medline and the Cochrane Library, a systematic review was conducted to address three questions regarding myocardial revascularization in these patients. These questions outline the current knowledge on this topic, current surgical strategies (off-pump vs. on-pump), and graft options (including hybrid techniques) utilized for revascularization. Three independent reviewers (MAE, DP, and AM) applied the inclusion criteria to all the included studies, obtaining the full texts of the most relevant studies. The reviewers subsequently assessed these articles to make the final decision on their inclusion in the review. Out of the initial 385 references, 156 were chosen for a detailed review. After examining the full articles were examined, 134 were found suitable for scoping review. Conclusion The literature notes the scarcity of surgical revascularization in LVD patients in randomized studies, with observational data supporting coronary revascularization's benefits. ONCABG is recommended for multivessel disease in LVD with LVEF < 35%, while OPCAB is proposed for older, high-risk patients. Strategies like internal thoracic artery skeletonization harvesting and postoperative glycemic control mitigate risks with BITA in uncontrolled diabetes. Total arterial revascularization maximizes long-term survival, and hybrid revascularization offers advantages like shorter hospital stays and reduced costs for significant LAD lesions.


Background
Ischemic cardiomyopathy (ICM) is defined as significantly impaired left ventricular function, specifically a left ventricular ejection fraction (LVEF) ≤40%, resulting from coronary artery disease (CAD) [1].Nevertheless, there is no consensus about a universal definition of this disease.In the following review, we will concentrate on patients with an ICM and LVEF ≤35%.This condition accounts for more than 60% of congestive heart failure cases and is linked to high morbidity and mortality, carrying a substantial risk of major cardiovascular events [2][3][4].
In patients with ICM, the treatment goals are prolonging survival, enhancing quality of life, and reducing the risk of both cardiac and noncardiac complications.Left ventricular dysfunction (LVD) in coronary disease patients is not necessarily irreversible.The underlying principle justifying the presumed benefit of revascularization is that augmenting blood supply to ischemic 'hibernating' myocardial segments ameliorates symptoms and regional ischemia and improves overall LV function and, consequently, clinical outcomes [3][4][5].Patients with ICM have been systematically excluded from the majority of randomized controlled trials (RCTs) concerning the management of chronic coronary syndrome.Hence, there is uncertainty regarding the applicability of published results to this patient population, and the evidence stems from observational studies [6].The 2021 ACC/ AHA guidelines [7] recommend surgical revascularization for patients with an ICM and LVEF <35% to improve survival [8,9].However, there are no specific recommendations regarding the optimal revascularization strategy for these patients.On the other hand the ESC/EACTS Guidelines [10] recommend surgical revascularization as the first line of treatment in this specific population when there is an acceptable surgical risk [8,[11][12][13] (see Table 1).
The primary objective of this review is to condense the current literature and disseminate research findings on variations in surgical techniques and graft options for myocardial revascularization in patients with LVD based on the latest evidence.

Methods
We conducted a scoping review following the Arksey and O'Malley methodology [24], encompassing the following five stages: 1) defining the research question; 2) identifying pertinent studies; 3) selecting studies; 4) organizing and extracting data; and 5) compiling, summarizing, and presenting the findings.
This scoping review serves as a comprehensive overview of an intricate area or one that has not been thoroughly reviewed previously, aiming to include all relevant literature regardless of study design [31].We used the following keywords to carry out this research: "Ischemic cardiomyopathy", "Coronary revascularization", "Surgical revascularization", "Left ventricular dysfunction", "Revascularization strategies", "Off pump", "Hybrid revascularization", "Arterial grafts", "Heart failure" and "Cardiogenic shock".
The main objective is to summarize and disseminate research findings on current knowledge, surgical techniques and graft options for myocardial revascularization in patients with left ventricular dysfunction and the current evidence in the literature.A secondary objective is patient selection for each surgical technique and the frequency of using a second arterial graft, total arterial revascularization or hybrid technique.
Aligned with these objectives, the following research questions were developed: What is the existing knowledge regarding surgical techniques for coronary Table 1 Overview of existing guidelines and supporting evidence of myocardial revascularization in patients with LVEF of 35% or less AHA Guidelines [7] ESC/EACTS Guidelines [10] Randomized controlled trials

Coronary artery bypass graft (CABG)
Class I: LVEF <35% without significant left main coronary artery disease.

Percutaneous coronary intervention (PCI)
Insufficient data.Class IIa: Single or two-vessel CAD when complete revascularization is achievable.Class IIa: Multivessel CAD, as per evaluation by the Heart Team considering coronary anatomy, expectation of complete revascularization, diabetic status, and comorbidities.
revascularization in patients with left ventricular dysfunction?What revascularization strategy (on pump vs. off pump) should be used in LVD?What graft options, including hybrid techniques, have better outcomes for revascularizing these patients?To ensure the selection of relevant literature, specific inclusion and exclusion criteria were formulated for all the retrieved data.
The inclusion criterion was: • Studies involving patients with ischemic left ventricular dysfunction (LVEF ≤35%).• Studies concerning revascularization strategies in patients with ischemic left ventricular dysfunction.• All the original studies, irrespective of study design, relevant systematic reviews and published American and European consensus guidelines.
The exclusion criterion was: • Studies focusing on patients with coronary artery disease but without left ventricular dysfunction.• Studies published in languages other than English.
• Opinion pieces, viewpoints, letters to the editor, conceptual frameworks, and conference abstracts.
Eligible studies were identified through searching the PubMed (MEDLINE database) bibliographical database and the Cochrane Library.Additionally, the reference lists of the included studies were scrutinized, relevant organizations were reviewed, and key journals were manually searched to identify further pertinent publications that might not have been captured in the initial search.
The application of the inclusion criteria to all the included studies was carried out independently by three reviewers (MAE, DP, and AM).Full articles were acquired for studies appearing most relevant to the research question.Subsequently, the reviewers evaluated the full articles to make the final decision on their inclusion in the review.In instances of potential discrepancies in articles inclusion, each reviewer independently assessed the eligibility criteria.Subsequently, consensus was sought through deliberation and referencing the established criteria.The reviewing team consisted of three members, and this decision was deliberate in order to maintain an odd vote (Fig. 1).

Main text
From the initial pool of 358 references, we narrowed the sample to 156 for a thorough review.After examining the full articles, 134 were determined to be suitable for inclusion in the scoping review.

Existing knowledge of myocardial revascularization in patients with LVD 35% or less
However, the optimal revascularization strategy for patients with CAD and severe LV dysfunction remains unclear [13].European guidelines recommend Class I CABG for multivessel or left main disease, in the presence of angina or heart failure, with acceptable surgical risk.PCI is recommended as a Class IIa indication in patients with one or two-vessel disease and could be considered as a Class IIa indication in patients with threevessel disease with a low SYNTAX score, considering the patient's expectation of complete revascularization, diabetic status, and comorbidities [10].AHA guidelines consider CABG for patients with moderate to severe LV dysfunction (35-50%) (Class IIa) and could be considered for severe LV dysfunction (LVEF <35%) (Class IIb) with significant left main disease.PCI is preferred as an alternative to CABG in selected stable patients with significant left main coronary disease, favorable anatomical conditions, or clinical characteristics predicting a significantly greater risk of adverse surgical outcomes [32].
Regarding evidence from clinical trials, the STICH trial [14] randomized 1,012 patients with ICM (LVEF <35%) to CABG plus optimal medical therapy (OMT) or OMT alone.At a median follow-up of 56 months, no significant differences were observed between the two arms in the primary outcome, defined as the rate of death from any cause.However, patients in the CABG group exhibited lower rates of cardiovascular death and death from any cause or hospitalization due to cardiovascular causes.In a subsequent analysis with a median follow-up of 9.8 years (STICH Extended) [8] a 16% reduction in all-cause mortality was found in the CABG group compared to the OMT group (P = 0.02).Subgroup analyses indicated that patients with 3-vessel CAD (P = 0.04) or severely remodeled LV (end-systolic LV volume index >78 mL/m2 or EF <27%: P=0.03) appeared to derive the maximum benefit from revascularization.
Nevertheless, a critical examination of the methodological limitations of the STICH trial is important.A considerable proportion of the study cohort exhibited either the absence of angina symptoms or a Canadian Cardiovascular Society (CCS) Angina Score of 1, a subjective parameter for ischemia assessment.Objective evaluations of ischemia, such as myocardial scintigraphy or stress echocardiography, were not provided.Consequently, the trial's ability to differentiate between patients exhibiting fibrotic myocardium and those with ischemic myocardium, thereby identifying candidates likely to benefit from revascularization, is questionable.Additionally, a STICH substudy with only 399 patients who underwent ischemic testing revealed no mortality benefit associated with revascularization, irrespective of the presence of ischemia [33].The inclusion of patients without regard to myocardial viability, despite the absence of evidence supporting the clinical efficacy of viability-guided revascularization, constitutes another notable limitation [25].Additionally, the substantial crossover rate of 17% potentially introduces bias, potentially underestimating the trial's results.
Myocardial viability testing can be performed with multiple imaging diagnostic techniques.Dobutamine Stress Echocardiography (DSE) assesses contractile reserve.Dobutamine can be used in low doses (5-10 μg x kg x min) or high doses (40 μg x kg x min) in order to evaluate the contractile reserve and showing promising predictive value for recovery post-revascularization [34], especially with a biphasic response [35].Another alternative is the Single Photon Emission Computed Tomography (SPECT), which along with the intake of radiotracers in myocardial cells offers valuable information on myocardial perfusion and viability [34,[36][37][38][39]. Positron Emission Tomography (PET) with the help of radiotracers bonded to glucose molecules provides superior spatial resolution.Distinguishing between irreversible injured and viable regions [40,41], relies on the perfusion and metabolism of myocardial cells, but it requires meticulous glucose control for accurate assessment [34].Another alternative is Cardiovascular Magnetic Resonance (CMR), that utilizing gadolinium chelated contrast agents, allows the precise detection of perfusion defects, microvascular obstruction and the transmurality of scar tissue with the most resolution [25,34,[42][43][44][45][46].This information aids to predict the functional recovery postrevascularization.This technique can also be performed along with dobutamine for stress testing [25,47].
Overall The STICH trial has been utilized by cardiologists and surgeons for over a decade to aid in decisionmaking for patients with LVD, however it is important to know its limitations.Nowadays, the above described methods to demonstrate ischemia and viability enable the heart team, especially the surgeon, to make judicious decisions for these patients who may benefit from surgical revascularization.
In the SYNTAX trial [48], at the 5-year follow-up, a more pronounced advantage was evident in complex lesions of 3 vessels or left main disease with CABG, and at 10 years of follow-up, the advantage persisted in 3-vessel disease [49].However, the patients with ICM and an initial LVEF ≤30% constituted a minority within the CABG cohort, accounting for only 2.5% compared to a mere 1.3% in the PCI group.
The HEART trial [50] was originally intended to enroll 800 patients with ICM and severely reduced LVEF (<35%) with residual myocardial viability according to conventional imaging, such as stress echocardiography with dobutamine, angiocardiography, and positron emission tomography (PET).Patients were assigned to OMT or invasive management of revascularization via angioplasty and/or CABG.Only 138 patients were ultimately randomized, and no significant differences were found between patients assigned to one of the management strategies at the 5-year follow-up.
A meta-analysis comparing different revascularization methods (PCI vs. CABG vs. OMT) in patients with coronary artery disease and an LVEF ≤40% demonstrated a significant reduction in mortality with revascularization strategies versus OMT.Moreover, among the revascularization strategies, CABG appears more favorable than PCI [13].This is attributed to higher survival rates and lower rates of repeat revascularization or reinfarction post-revascularization, albeit with a higher risk of stroke with a minimum follow-up of at least 12 months.However, this does not specify the surgical revascularization technique under which this benefit is observed.
Available evidence supports CABG over PCI in patients with CAD and severely depressed LV systolic function, although the benefit of CABG over OMT seems to become significant only later during long-term followup [6].A limitation of these trials is that medical therapy did not include modern medications, such as angiotensin receptor/neprilysin inhibitors or sodium-glucose cotransporter 2 inhibitors, which have demonstrated a greater impact on major cardiovascular outcomes.
Patients with left ventricular dysfunction pose the greatest challenges and complexities in coronary surgery, with risk scores indicating a high prediction of mortality.This is due to the high likelihood of complications, which increase the probability of early mortality.However, the clinical characteristics that render these patients complex also identify them as the population that could benefit the most from CABG [51].Additionally, risk scores are not specifically tailored for patients with severe left ventricular dysfunction, hence, their prediction may not accurately reflect the real risk [52].
Most of the evidence supporting myocardial revascularization in ischemic cardiomyopathy (ICM) originates from observational studies, with conflicting data from a limited number of RCTs (see Table 2).Based on this information, guidelines recommend CABG as the preferred revascularization strategy without specifying which technique is most beneficial for these patients.

Off-pump vs on-pump surgery
Patients undergoing CABG for LVD constitute a less studied subgroup, with studies beginning in 1990 [53,54] leading to increased experience with this group and the development of various available revascularization techniques.Since then, the off-pump coronary artery bypass grafting (OPCABG) technique has shown promise in achieving complete revascularization [55].Particularly in a high-risk patient subgroup [56], multiple studies have demonstrated positive outcomes of OPCABG in these patients [57][58][59].This technique avoids obligatory global myocardial ischemia from aortic cross-clamping, cardioplegia arrest, and systemic inflammation, which are especially detrimental in high-risk patients [60].This approach significantly reduces intraoperative organic damage due to the postcardiopulmonary bypass inflammatory response, particularly to the myocardium, kidneys, liver, and lungs, thereby improving outcomes in patients with preoperative organ dysfunction (see Table 3) [61].
Subsequently, several studies have evaluated these two techniques in patients with ischemic cardiomyopathy and low LVEF , yielding diverse results.Shennib et al. [58] found no significant differences in outcomes or complete revascularization between 77 patients treated with LVD and those treated with either technique.The ROOBY trial [62] concluded that short-term outcomes did not differ between on-pump coronary artery bypass grafting (ONCABG) and OPCABG, but the long-term mortality risk was greater with OPCABG.However, the trial was criticized for its selection of surgeons who performed the procedures, and there was also an underrepresentation of patients with LVD, accounting for only 5.7% of the total population.
Keeling et al. [55] reported data from the STS database registry comparing 25,667 patients with LVD who underwent ONCABG (79.9%) versus OPCABG (20.1%).In the OPCABG subgroup, more comorbidities and a greater predicted preoperative mortality risk were observed, but a better incidence of distal anastomoses was noted with this technique.However, compared with those of ONCABG, lower rates of in-hospital mortality and postoperative neurological events and decreased prolonged ventilation were observed.These improved postoperative outcomes of OPCABG could be explained by the reduced need for intraoperative transfusions [65] and the absence of global ischemia as well as the shorter surgical time [55].Despite the fewer distal anastomoses, recent data showed that, in older adults, surgery did not increase allcause mortality given the preoperative risk profile [66].
In the CORONARY trial, 4752 patients randomized to OPCABG or ONCABG were evaluated, with 23% having LVD.A subgroup analysis comparing patients based on the EuroSCORE [63] revealed that, in low-risk patients (EuroSCORE 0-2), there was a trend toward worse 1-year mortality with OPCABG.Conversely, in high-risk patients (EuroSCORE ≥3), better outcomes were observed with OPCABG [67].One possible   interpretation is that in low-risk cases, events related to cardiopulmonary bypass (CPB) are rare, as are technical adverse events such as incomplete revascularization or a decrease in graft permeability.Conversely, in highrisk patients, adverse events related to CPB and aortic manipulation are more common, surpassing the risks associated with technical adverse events [68].Based on this premise, they concluded that preferring ONCABG in low-risk patients and OPCABG in medium-to high-risk patients was reasonable [63].
When the ROOBY Follow-up Study was published [64], no advantage of OPCABG in terms of outcomes or costs was found after 10 years of follow-up.Slightly shorter revascularization-free survival times were observed, but no additional benefits were found in high-risk patients.The authors highlighted that both techniques are complementary and are part of the revascularization possibilities; however, there is no reason to prefer one technique over the other for candidates suitable for both techniques.Nevertheless, even in patients with extreme LVD (LVEF 10-20%), patients could undergo OPCABG with a reasonable mortality rate (11%) and achieve excellent long-term results, reaching an average LVEF of 35% at the 1-year follow-up, as described by Carr et al. [69].Moreover, this technique is considered a viable option in special populations, such as patients on hemodialysis [70] or diabetic patients [71], with a high burden of aortic atherosclerotic disease and a high risk of stroke, where the use of the ' Aorta non-touch' technique [72,73] under OPCABG minimizes postoperative cerebrovascular complications.
In the context of OPCABG, the use of a preoperative intra-aortic balloon pump (IABP) has also been described in high-risk patients, as this improves cardiac performance and facilitates access to target vessels while maintaining hemodynamic stability [74,75].The beneficial effects of IABP include reducing ventricular afterload, improving coronary diastolic perfusion, and enhancing subendocardial perfusion, all of which contribute to maintaining hemodynamic stability during surgery [76].Additionally, there is reported redirection of blood flow to ischemic myocardial areas, improved graft flow post-bypass, decreased ventricular arrhythmias, and a decreased rate of low cardiac output postoperatively have been reported, thereby reducing end-organ dysfunction [77].One of its downsides involves vascular complications related to IABP, which occur in up to 15% of high-risk patients, especially in women, diabetic patients, smaller patients, and those with peripheral vascular disease [78].These complications could be mitigated by assessing the status of the thoracic and abdominal aortas through angiography or CT scans beforehand, maintaining coagulation levels for more than 150 seconds with heparin, and shortening the IABP duration by removing it immediately after the procedure, whenever possible [76].
It is important to consider the technical aspects of OPCABG surgery to facilitate procedural efficacy.Among the most discussed are intracoronary shunts and the CO2 blower.Intracoronary shunts are utilized to sustain blood flow in the distal circulation while constructing coronary anastomoses, thereby preventing inadvertent suturing of the posterior walls.However, proximal vessel occlusion has improved time and visualization.Additionally, the use of humidified CO2 blowers aids in enhancing arteriotomy visualization, playing a critical role in the precise construction of anastomoses [68].

Hybrid revascularization
For patients with multivessel coronary disease, both CABG and PCI are considered definitive treatments [79][80][81].However, CABG has proven to be particularly effective in patients with left anterior descending artery (LAD) disease, owing to the established benefits of the left internal thoracic artery (LITA) graft to the LAD [82].Hybrid coronary revascularization (HCR) combines the use of LITA-to-LAD anastomosis with PCI intervention for other non-LAD diseased coronary arteries [83].
The HCR is based on the known long-term benefits of CABG with LITA grafts to the LAD in patients with severe and complex LAD disease, as well as the advantages of PCI over saphenous grafts for non-LAD lesions [84].HCR is described in two distinct ways: one involving simultaneously performing both procedures in a hybrid operating room and the other through staged approaches (see Table 4).Better outcomes are attributed to simultaneous complete revascularization, as in staged approaches, the period of incomplete revascularization is prolonged, increasing the risk of adverse cardiovascular events [84].
There is limited data on the durability of HCR compared to that of conventional CABG.In a multicenter observational study, Harskamp et al. [85] compared mortality and complications between HCR and CABG in patients from The Society of Thoracic Surgeons (STS) Adult Cardiac Surgery Database, including 198,622 patients (0.48% HCR and 98.5% CABG), finding no significant differences in mortality or the composite of in-hospital mortality and complications.Similarly, Harskamp et al. [86] conducted a meta-analysis of 6 studies (1 case-control study and 5 propensity score-adjusted studies) involving 1,190 patients (30.8% HCR and 69.2% CABG), again revealing no differences in mortality or in the composite of in-hospital mortality and complications, however, HCR showed higher rates of repeat revascularization at 1 year.Zhu et al. [87] also performed a meta-analysis of 10 cohort studies involving 6,176 participants and found no differences in major adverse cardiovascular or cerebrovascular events or mortality up to the 1-year follow-up.
Hannan et al. [83] conducted a multi-institutional study involving 37,589 patients with multivessel disease (0.80% HCR and 99.2% CABG).The authors reported that HCR is seldom used as an alternative to CABG in patients with multivessel disease.Furthermore, after propensity score matching, they found that at 6 years, HCRs were associated with increased mortality (19.1% vs 14.2%) and a greater rate of repeated revascularization in the LAD artery, as well as in areas where percutaneous intervention was performed (23.4% vs 11.8%).
In fact, HCR might be an acceptable approach in the short term (1 year), especially when performed simultaneously.In the short term, patients have a lower risk of major adverse cardiovascular events (MACEs), including mortality, stroke, and myocardial infarction.Likewise, when performed in a scheduled manner, there is a reduced risk of transfusions and repeated revascularization.However, when evaluating long-term outcomes (6 years), a higher mortality rate and an increased need for repeated revascularization compared to CABG become evident (see Table 5) [84].

Graft options for patients with ICM
Surgical revascularization seems to be the optimal choice for these patients.However, there are no international guideline recommendations regarding which grafts provide the greatest benefit to these patients or increase the likelihood of better outcomes.Therefore, a search was conducted for available information (see Table 6).
Performing CABG using a LITA graft is an effective approach for treating patients with advanced and symptomatic CAD [26] and has shown superiority to PCI in severe CAD and diabetic patients [27].This superiority is attributed to better long-term patency and survival than those of saphenous vein grafts (SVGs) [28].The latter are mainly responsible for graft failure and exhibit intimal fibrosis and accelerated atherosclerosis, which can reduce graft patency by up to 50% at 10 years, compromising long-term outcomes [26,29,30].Hence, exploration of the use of CABG with multiple arterial grafts has continued, as such use significantly impacts mortality [26].These arterial grafts are living tissue that displays adaptive mechanisms increasing blood flow and shows resistance to atherosclerosis through nitric oxide release, as well as protection against proximal CAD progression [107,108].
LVD is strongly associated with perioperative mortality [109].The priority in these patients is to mitigate surgical risk [110].The use of multiple arterial grafts may increase the complexity and duration of surgery, which may not be well-tolerated by patients with LVD [111] and is associated with increased mortality [52].However, retrospective analyses have shown comparable operative safety between bilateral internal thoracic artery (BITA) use and single internal thoracic artery (SITA) use.Observational studies present conflicting information regarding longterm survival with BITA in this patient population [88][89][90]112].Although BITA is not routinely employed in LVD patients, it could be considered in selected scenarios guided by anticipated patient survival and the judgment and experience of the surgeon.
The use of the BITA strategy, utilizing the right internal thoracic artery (RITA) as a second arterial conduit, has been shown to be an independent survival factor compared to the use of the SVG [91].In nearly all patients where BITA is technically feasible, a significant longterm survival benefit has been observed, leading to freedom from recurrent myocardial infarction and angina for up to 15 years [72,92,113].An observational study from the Cleveland Clinic by Lytle et al. [88], as well as a metaanalysis of observational studies by Yi et al. [114], demonstrated that survival curves between SITA and BITA start diverging in favor of BITA revascularization at the 10th year of follow-up.Consequently, the hemodialysis patient group did not show apparent survival benefits with BITA grafting due to their relatively short life expectancy [70].Its maximum benefit is achieved when using the RITA as a graft to the lateral wall rather than the right coronary artery (RCA) [93].The only randomized study, the ART     .However, potential confounding factors, such as the use of the radial artery (RA) as the second conduit in the SITA group, high adherence to guideline-directed medical therapy, and short follow-up time, were considered [26].However, its use has not been universally accepted due to the association of BITA usage with an increased risk of sternal complications, including deep sternal wound infections (DSWI) and poor sternal healing due to decreased sternal perfusion [91,[94][95][96][97].This risk is even greater in older patients, women, diabetic individuals and morbidly obese patients with a glycosylated hemoglobin (HbA1c) level >7.5%, with up to a 10-fold increase in the risk of DSWI [71,115].This risk has been mitigated by using the skeletonized BITA grafting technique to preserve sternal perfusion via collateral vessels [116], as well as by strictly controlling perioperative glucose levels through insulin infusions [96,117,118].Hyperglycemia in the first two postoperative days is considered an independent predictor of DSWI development [118].Multiple studies have shown that maintaining glucose levels <180 mg/dL with insulin infusions during surgery and in the early postoperative days, along with skeletonization, reduces the incidence of DSWI [118][119][120].However, perfusion disturbances persist, as confirmed by SPECT perfusion tests, indicating a potential risk of sternal infection, especially in elderly and diabetic patients [116].
CABG with BITA is typically limited to patients <75 years old with suitable coronary targets [72].Age is considered a limiting factor due to increased osteoporosis incidence, a greater proportion of diabetic patients, and a greater risk of stroke [121].However, multiple studies have shown no differences in long-term survival up to the age of 79 years [30,92,96,98,99].For high-risk patients, particularly those who are diabetic and elderly, a nontouch off-pump technique is considered, where avoiding aortic manipulation reduces the risk of postoperative stroke [72,73].This technique also decreases operative mortality and morbidity, especially in elderly patients or those with poor cardiac function [99].
Similarly, the use of the RA as a second or even third arterial conduit in an all-arterial revascularization strategy has been proposed.It is recommended to harvest from the side with better ulnar compensation and arterial quality, rather than from the nondominant side.Harvesting is usually well tolerated, with possible self-limiting and transient occurrence of paresthesia and pain [122].Contraindications for its use include upper extremity vascular diseases; prior forearm trauma, especially if it requires surgical repair; and previous forearm or wrist surgeries [111].Furthermore, in patients with chronic kidney disease, the potential benefit of CABG with an RA graft should be weighed against the possible need for an upper limb arteriovenous fistula for dialysis, although limited evidence exists to guide this decision [111].
Compared to SVG, the RA was associated with a significantly lower incidence of adverse cardiac events (HR 0.67, 95% CI 0.49 -0.90) and a reduced incidence of occlusion (HR 0.44, 95% CI 0.28 -0.70), with improved patency at 5 years [100].RA is considered an alternative for mitigating or reducing the risk of DSWI associated with BITA [98].Several authors have reported that RA is superior to RITA [101,102], while others have indicated the opposite [103].However, when comparing RA to RITA, there are no differences in graft patency, survival rate, or event-free survival rate, but differences exist in DSWI incidence and operative time, which tend to be longer with BITA [73].Nevertheless, there was an underrepresentation of patients with LVD, with only 3% of patients having a low LVEF.Compared to SVG, RA exhibits superior patency and better clinical outcomes at 5 years [52].There are RCTs such as the RAPCO Trial [104], which compares RA, BITA, and SVG patency at 10 years, and the RAPS [105], which compares RA and SVG patency at 5 years.However, these trials lack representation of patients with LVD, making their findings challenging to apply in this patient population.Jung et al. [106] demonstrated better patency rates when RA was used as a graft when directly anastomosed to the ascending aorta than when it was anastomosed to the side of the LITA, with patency rates of 85.3% vs. 65.2%,respectively, at 5 years.According to the most recent myocardial revascularization guidelines, the use of the RA for severe stenosis targets is proposed as a Class I recommendation with Level B evidence, while the BITA is a Class IIa recommendation with Level B evidence [10,123].Additionally, lesser-used grafts, such as those from the gastroepiploic artery (GEA) or the inferior epigastric artery (IEA), have been employed as third conduits, albeit less frequently and in nonmain branches [91,94,95,97,99].Concerning all-arterial revascularization, significantly longer survival has been observed in patients receiving 3 arterial conduits than in those receiving 2 or 1 arterial conduit (HR 0.8, 95% CI 0.75 -0.87), attributed to their greater long-term patency and lower association with major cardiovascular events [123].
In conclusion, according to multiple studies, there is an underrepresentation of the population with LVD, constituting a very small portion of the total population and being an exclusion criterion in some studies.However, these patients also benefit from using CABG with a second arterial conduit, either BITA or RA revascularization [92,98].This subset includes those who benefit the most from arterial revascularization [88], This incremental benefit becomes apparent early after surgery and persists during follow-up [99].Performing OPCABG with in situ leftsided skeletonized BITA grafting is safe and feasible, with a decreased association with operative mortality and morbidity in patients with low cardiac function [56,68,99].
As previously indicated ICM accounts for more than 60% of the congestive heart failure cases, associated with high morbidity and mortality.However, this condition is not necessarily irreversible [2][3][4].Revascularization of ischemic myocardial segments can lead to an improvement in overall LV function and consequently, better clinical outcomes [3][4][5].Numerous studies have shown that revascularization can result in an improvement in LVEF in up to 60% of patients, with a wide range of improvement observed [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].The objective of this review was to explore the variations in surgical techniques and graft options for myocardial revascularization of LVD patients that lead to the aforementioned LVEF improvement.This prompts the question: What is the clinical significance of an improvement in LVEF for patient-important outcomes?These outcomes are defined as "a characteristic or variable that reflects how a patient feels, functions or survives" [124][125][126].As previously stated in ICM patients the treatment goals are prolonging survival, enhancing quality of life and reducing the risk of cardiac and noncardiac complications.
The latest consensus statement of a universal definition for HF written by the Heart Failure Society of America (HFSA), Heart Failure Association of the European Society of Cardiology (HFA/ESC) and the Japanese Heart Failure Society (JHFS) created a novel entity of patients with heart failure with improved ejection fraction (HFimpEF).These were originally patients with LVD with a second measurement of LVEF >40% and a ≥10% increase from baseline LVEF of ≤ 40% [127].Some studies show that HFimpEF patients had a better prognosis and a significant improvement in health-related quality of life [128,129], however other concluded that the difference in the risk of death between patients with HFimpEF and heart failure with reduced ejection fraction (HFrEF) groups was not statistically significant [130] In a meta-analysis from He at al. [131] nine studies of 9491 heart failure patients were included and during a followup of 3.8 years, the pooled prevalence of who develop HFimpEF after treatment was 22.64%.HFimpEF reduces the risk of all cause mortality by 56%, cardiac hospitalization by 60% and composite events by 44% compared to patients with HFrEF.However this study had several limitations with an absence of a unified definition of HFimpEF, the lack of enough data to perform a subgroup analysis and the absence of randomized controlled trials.
In more recent studies, Wohlfart et al. [129] showed that recovery of systolic function was associated with HF-associated quality of life (QoL) improvements and for each 10% increase in LVEF, the Kansas City Cardiomyopathy Questionnaire score improved by a mean (SD) of 4.8 土 1.6 (p = 0.003).Likewise, DeVore et al. [132] reported QoL improvements related to ≥10% increase in LVEF in patients with initial HFrEF with a mean change of 7.6 points (range 6.0 -9.2) in the Kansas City Cardiomyopathy Questionnaire compared with 3.5 points (range 2.3 -4.8) in the non-HFimpEF (p < 0.001).In a study from Zamora et al. [133] the HFimpEF group had shorter HF duration and a larger proportion of patients classified as NYHA I-II.Also the perceived QoL improvement in patients with HFimpEF was mainly related to the number of HF-related hospitalizations in the previous year and NYHA functional class.Consideration must be given to the fact that QoL is inherently subjective and can be influenced by numerous factors, such as age, sex, previous hospitalizations, diabetes and treatments.The physical dimension is very important, patients with more comorbidities or higher NYHA functional classes reported worse QoL scores [133].
Several limitations need to be acknowledged in our study.As previously mentioned the majority of RCT exclude patients with ICM.The scarcity of RCTs in the existing literature that fulfill the inclusion criteria made us recur to observational studies with an underrepresentation of ICM patients, susceptible to bias.Also, the lack of a universal definition of LVD patients among the studies, the complexity of the topic and the heterogeneity of outcomes reported in the existing literature made a comprehensive assessment challenging.Therefore the best approach to overview and synthesize the available evidence was to perform a scoping review.Further RCT studies are necessary to assess the potential benefits of the available surgical approaches and graft options described in the literature.Also further randomized studies are required to explore the clinical significance of an improvement in LVEF and its impact on patientimportant outcomes.To our knowledge there is an ongoing RCT, the MASS VI VF, which includes patients with multivessel CAD, angina pectoris and LVD (≤35%) and ≥10% ischemia detected by myocardial scintigraphy.The objective of this study is to randomize 300 patients to myocardial revascularization surgery and 300 patients to medical treatment only in order to evaluate if myocardial revascularization contributes to a better prognosis compared with those treated with OMT [134].
Patients with LVD and LVEF ≤35% have shown improvement after surgical revascularization, as demonstrated in this article.This LVEF improvement has also been strongly correlated with enhancements in quality of life and reductions in mortality rates.Future studies should prioritize refining the methodologies of current published trials by addressing both clinical and imaging indicators of myocardial viability, as well as implementing long-term follow-ups of revascularized patients.It is also essential to determine the method of follow-up, whether it should involve clinical assessments or less invasive imaging modalities.The advancements in coronary CT and MRI hold promise for the future, potentially aiding in the evaluation of graft patency and providing accurate quantification of LVEF, while being less invasive.Regarding patients presenting with acute coronary syndrome and LVD with an LVEF ≤ 35%, this remains another topic for review.It is still unclear whether these patients should be analyzed within this group.

Conclusions
In conclusion, the literature highlights the scarcity of ischemic left ventricular dysfunction patients in randomized studies, with observational studies predominating.However, existing data support the benefits of coronary revascularization in LVD, evidenced by improved LVEF and QoL.
ONCABG is recommended for multivessel disease in patients with LVD and LVEF < 35%, with LITA-to-LAD graft providing significant benefits.Angina and/or demonstrated myocardial ischemia are necessary for better outcomes.
OPCAB is proposed for older, higher-risk patients, with the aorta-non-touch technique reducing stroke risk.Preoperative IABP use may improve outcomes.It must
• Harvesting with the use of skeletonized technique.
No anticipation to perform a redo sternotomy.

Diabetic patients.
High risk patients for DSWI.Patients without upper extremity artery disease.Patients where it is anticipated the need of a redo sternotomy.
be kept in mind that this technique is not suitable for all surgeons or all patients, but it results in excellent outcomes when applied correctly.SVG occlusion risk prompts consideration of a second arterial graft or complete arterial revascularization.RITA and RA involve specific considerations, with similar longterm patency rates.Techniques like skeletonization harvesting and postoperative glycemic control can mitigate risks associated when using BITA in uncontrolled diabetes.For patients at high risk of redo sternotomy, techniques like covering the RITA graft with a Dacron graft or passing it through the transverse sinus may mitigate risks.The radial artery is preferred in uncontrolled diabetes and when its preservation is unnecessary for vascular access, such as in hemodialysis patients.Total arterial revascularization is advocated for maximizing long-term survival compared to single or double arterial grafting methods.
Hybrid revascularization remains an alternative for patients with significant LAD lesions and other suitable lesions for percutaneous revascularization.While clear recommendations are lacking, multidisciplinary decisions are suggested, offering advantages like shorter hospital stays and reduced costs.

Table 2 (continued) Study Title / First Author Year of Publication Sample Size / Follow Up Study Objective Study Main Conclusion
CABG Coronary artery bypass grafts, MT Medical therapy, LVEF Left ventricular ejection fraction, CAD Coronary artery disease, LVD Left ventricular dysfunction, SVR Surgical ventricular reconstruction, LVESVI Left ventricular end-systolic volume index

Table 3
Evidence comparing ONCABG versus OPCABG in patients with Left Ventricular Dysfuntion

Table 5
Evidence supporting hybrid revascularization in LVD

Table 6
Evidence supporting graft options in patients with LVD

Table 7
Indications for different surgical revascularization strategies and graft options SIHD Stable ischemic Heart Disease, CAD Coronary artery disease, LITA Left internal thoracic artery, LAD Left anterior descending artery, SVG Saphenous vein graft, PAD Peripheral artery disease, LEF Low ejection fraction, SITA Single internal thoracic artery, HbA1C Glycosylated hemoglobin, DSWI Deep sternal wound infection Higher predicted risk of mortality score.Patients with moderate to high-risk score (EuroSCORE ≥ 3).To minimize risk of stroke, renal failure, blood transfusions, respiratory failure and development of atrial fibrillation.To minimize midterm cognitive dysfunction.Use of preoperative IABP in patients with severe LVD allows complete revascularization.